Engineering the adenovirus genome to allow the insertion of foreign genes may yield infectious recombinant viruses that express the foreign genes. Such recombinants could potentially be used as vaccines. We have made some progress in this approach including the growth and purification of adenovirus types 4 and 7 from large suspensions, the isolation and restriction mapping of their genomes and the cloning in plasmids of the E3 region and adjacent areas of the adenovirus 4 genome. The right hand end of the adenovirus 4 genome (map units 83-100) has also been cloned. The ends of the available clones have been sequenced and primers have been synthesized to localate the major late promoter and the tripartite leader sequences. The VP7 glycoprotein gene of several rotavirus strains and part of the fourth rotavirus gene (the area which encodes VP8 and a portion of VP5) have been cloned in pBR322 or in the polylinker area of pUC vectors to facilitate their transfer into the adenovirus genome.